Liquid circulating device and medical apparatus

ABSTRACT

A liquid circulating device includes a pump chamber whose volume is changed by a volume changing unit; an inlet channel that is an inflow passage of the liquid to the pump chamber; a liquid resistance element; an outlet channel; a circulation channel of a length L through which the liquid circulates from the outlet channel to the inlet channel; and a pressure regulating mechanism that contains the liquid of a volume Vb during the non-operation of the volume changing unit and supplies the contained liquid as part of the circulating liquid during the operation of the volume changing unit. When the compliance of the circulation channel is defined as Cs, and the pressure of the liquid in the circulation channel at the position of a length x from the outlet channel during the operation of the volume changing unit is defined as P(x), the volume Vb satisfies a predetermined relationship.

BACKGROUND

1. Technical Field

The present invention relates to a liquid circulating device.

2. Related Art

In the related art, a technique using a liquid circulating device is known as the technique for adjusting the temperature of an object (for example, JP-A-8-242463). This technique brings a circulation channel, through which a liquid circulates, into contact with a target (hereinafter referred to as a temperature adjustment target) whose temperature is intended to be adjusted, and adjusts the temperature of the temperature adjustment target depending on the temperature of the liquid that is circulated. However, since the liquid circulating device of the related art is not configured in consideration of the pressure inside the circulation channel during the operation, problems that occur, depending on operating conditions, are for example, the cross-sectional area of the channel becomes small, and a decrease of circulation efficiency of the liquid have been pointed out.

SUMMARY

An advantage of some aspects of the invention is to ensure stability of circulation efficiency.

The invention can be implemented as the following forms or application examples.

Application Example 1

Application Example 1 is directed to a liquid circulating device that circulates a liquid in non-contact with the atmospheric air. The liquid circulating device includes a pump chamber whose volume is changed by a volume changing unit; an inlet channel that is an inflow passage of the liquid to the pump chamber; a liquid resistance element that controls or stops the flow of the liquid that flows from the pump chamber to the inlet channel; an outlet channel that is an outflow port of the liquid from the pump chamber; a circulation channel of a length L through which the liquid circulates from the outlet channel to the inlet channel; and a pressure regulating mechanism that contains the liquid of a volume Vb during the non-operation of the volume changing unit and supplies the contained liquid as part of the circulating liquid during the operation of the volume changing unit. When the compliance of the circulation channel is defined as Cs, and the pressure of the liquid in the circulation channel during the operation of the volume changing unit at the position of a length x from the outlet channel is defined as P(x), the volume Vb satisfies the relationship of Formula (3).

$\begin{matrix} {{Vb} \geq {\gamma \frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot {P(x)}}\ {{x\left( {\gamma \geqq 0.8} \right)}}}}}} & (3) \end{matrix}$

According to this liquid circulating device, the pressure regulating mechanism supplies the liquid of a volume Vb contained in the pressure regulating mechanism, as part of the circulating liquid that circulates through the circulation channel, during the operation of the volume changing unit. Accordingly, the pressure inside the circulation channel during the operation of the volume changing unit can be kept from dropping significantly. Additionally, when γ is set to one or more and the liquid of the volume Vb is contained in the pressure regulating mechanism, the value of the pressure P(x) inside the circulation channel during the operation of the volume changing unit can be kept from becoming equal to or lower than the pressure inside the circulation channel during the non-operation of the volume changing unit. Accordingly, the circulation efficiency can be stably secured.

Application Example 2

In the liquid circulating device according to Application Example 1, the volume Vb may satisfy the relationship of Formula (4) when the pressure of the liquid that flows out to the circulation channel from the outlet channel is defined as Ps.

Vb≧γ½Cs·Ps

(γ≧0.8)  (4)

According to this liquid circulating device, the pressure regulating mechanism supplies the liquid of a volume Vb contained in the pressure regulating mechanism, as part of the circulating liquid that circulates through the circulation channel, during the operation of the volume changing unit. Accordingly, the pressure inside the circulation channel during the operation of the volume changing unit can be kept from dropping significantly. Particularly, if γ is set to one or more and the liquid of the volume Vb is contained in the pressure regulating mechanism, the pressure inside the circulation channel during the operation of the volume changing unit can be more reliably kept from becoming equal to or lower than the pressure inside the circulation channel during the non-operation of the volume changing unit.

Application Example 3

In the liquid circulating device according to Application Example 1 or 2, the pressure regulating mechanism may include a liquid containing chamber that contains the liquid to be used for the supply, and may be deformable according to the amount of the liquid contained inside the liquid containing chamber.

According to this liquid circulating device, the liquid containing chamber that is deformable according to the amount of the liquid contained therein is used as the pressure regulating mechanism. Thus, the internal pressure can be maintained in a predetermined range even if the amount of the liquid contained therein changes.

Application Example 4

In the liquid circulating device according to Application Example 3, the liquid containing chamber may be a pack formed by sealing films in the shape of a bag.

According to this liquid circulating device, the pack is used as the pressure regulating mechanism. Thus, a configuration in which the liquid can be easily supplied can be provided.

Application Example 5

In the liquid circulating device according to Application Example 4, the liquid containing chamber may be attachable to and detachable from the liquid circulating device.

According to this liquid circulating device, the liquid containing chamber is attachable and detachable. Thus, only the liquid containing chamber can be replaced.

Application Example 6

In the liquid circulating device according to any one of Application Examples 1 to 5, the pressure regulating mechanism may include a branch channel that branches from the circulation channel.

According to this liquid circulating device, the branch circuit is used as the pressure regulating mechanism. Thus, the liquid can be easily supplied.

Application Example 7

In the liquid circulating device according to Application Example 6, a sealing material that seals the contained liquid and moves according to the pressure differential between the pressure of the liquid within the branch channel and atmospheric pressure may be arranged inside the branch channel.

According to this liquid circulating device, the sealing material is arranged in the branch channel. Thus, the liquid can be prevented from flowing out of the branch channel. Since the sealing material moves according to the pressure differential between the pressure of the liquid within the branch channel and the atmospheric pressure, the internal pressure can be maintained in a predetermined range.

Application Example 8

In the liquid circulating device according to Application Example 7, the liquid may be a first liquid, a second liquid that is phase-separable from the first liquid, and may be sealed between the first liquid and the sealing material inside the branch channel, and the vaporization heat of the second liquid may be greater than the vaporization heat of the first liquid.

According to this liquid circulating device, the first liquid can be kept from evaporating from the branch channel.

Application Example 9

In the liquid circulating device according to any one of Application Examples 1 to 8, the volume changing unit may use an operating element that operates depending on a change in voltage.

According to this liquid ejecting apparatus, a change in the volume of the pump chamber can be electrically controlled.

Application Example 10

Application Example 10 is directed to a medical apparatus using the liquid circulating device according to any one of Application Examples 1 to 9.

According to this medical apparatus, a liquid circulating device that stably ensures the circulation efficiency can be used.

Application Example 11

Application Example 11 is directed to a liquid ejecting apparatus using the liquid circulating device according to any one of Application Examples 1 to 9.

According to this liquid ejecting apparatus, a liquid circulating device that stably ensures the circulation efficiency can be used.

In addition, the invention can be realized in various aspects. For example, the invention can be realized in forms of a liquid circulating system, a temperature adjusting device, or the like, other than a liquid circulating method and a liquid circulating device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is an explanatory view showing the schematic configuration of a liquid ejecting system.

FIG. 2 is a schematic view schematically showing the configuration of a liquid circulating device.

FIGS. 3A to 3C are explanatory views showing the flow of a liquid inside a circulating pump.

FIGS. 4A to 4D are explanatory views showing the configuration of a film pack.

FIG. 5 is an explanatory view illustrating a liquid channel where internal pressure is appropriately maintained.

FIG. 6 is an explanatory view illustrating the configuration of a branch channel.

FIGS. 7A to 7C are explanatory views illustrating Modification Example 6.

DESCRIPTION OF EXEMPLARY EMBODIMENTS A. First Example A1. System Configuration:

Embodiments of the invention will be described on the basis of examples. FIG. 1 is an explanatory view showing the schematic configuration of a liquid ejecting system 10 as one example of the invention. The liquid ejecting system 10 is equipped with a liquid ejecting apparatus 20 and a liquid circulating device 100 that cools the liquid ejecting apparatus 20. The liquid ejecting apparatus 20 is a water jet knife that ejects a jet water stream to living body tissues, such as the skin. Particularly, the liquid ejecting apparatus 20 of the present example is a water jet pulse scalpel that exfoliates and incises living body tissues.

The liquid ejecting apparatus 20 is equipped with a pulsation generator 30 that ejects a jet water stream, a liquid container 40 that contains water, a supply pump 42 that pumps the water contained in the liquid container 40 to supply the water to the pulsation generator 30, a connecting tube 44 that connects the liquid container 40 and the supply pump 42, and a connecting tube 46 that connects the supply pump 42 and the pulsation generator 30.

The pulsation generator 30 is equipped with a liquid chamber 32 that temporarily stores the water supplied from the connecting tube 46, a piezoelectric actuator 34 that imparts pulsation to the water stored in the liquid chamber 32, a liquid ejecting pipe 36 that communicates with the liquid chamber 32 and allows the water to which pulsation is imparted by the piezoelectric actuator 34 to pass therethrough, a lower case 38 that houses the piezoelectric actuator 34 therein, and an upper case 39 that constitutes the liquid chamber 32 and is connected to the lower case 38.

The piezoelectric actuator 34, which is a laminated piezoelectric element, changes the volume of the liquid chamber 32 by deforming a diaphragm using the piezoelectric effect of a piezoelectric element. If the volume of the liquid chamber 32 becomes small, the water stored in the liquid chamber 32 is ejected to the outside as a jet water stream through the liquid ejecting pipe 36. Additionally, as another means for changing the volume of the liquid chamber 32, a piston may be driven and the volume of the liquid chamber 32 may be changed by the displacement of the piston.

The liquid circulating device 100, which is an apparatus that cools the piezoelectric actuator 34 of the liquid ejecting apparatus 20, is equipped with a circulating pump 110, and a liquid channel 190 that is a circulation channel having both ends connected to the circulating pump 110. The liquid channel 190 is a tube that has pressure resistance and flexibility. Although medical tubes or general industrial tubes that are made of, for example, fluorine-based resins, such as PTFE, polyimide-based resins, thermoplastic resins, such as PVC-based resins, or silicone rubber are applicable as the tube, the invention is not particularly limited thereto. The liquid channel is wound around the piezoelectric actuator 34. For this reason, the heat generated in the piezoelectric actuator 34 is transmitted to the liquid (circulation liquid) that circulates through the inside of the liquid channel 190, and the piezoelectric actuator 34 is cooled. The circulation liquid whose temperature has risen is cooled by air-cooling while circulating through the liquid channel 190. In addition, the circulation liquid may be separately cooled using a radiator. In the present example, the circulation liquid is a liquid in consideration of the efficiency of heat exchange. In the liquid circulating device 100, various liquids, such as water or oil, can be adopted as the liquid. For example, if silicone oil with low volatility and specific viscosity is adopted in the liquid circulating device 100, the circulation liquid does not evaporate easily, and the liquid circulating device 100 that can be used for a long period of time can be provided.

FIG. 2 is a schematic view schematically showing the cross-sectional configuration of the liquid circulating device 100. In the present example, in the liquid circulating device 100, a hermetically closed circulation channel is constituted by the circulating pump 110 and the liquid channel 190. The hermetically closed circulation channel means a circulation channel that does not have a portion where the circulation liquid comes in contact with the outside (atmospheric air). By adopting the hermetically closed circulation channel, bubbles, other foreign matter, or the like can be prevented from being mixed with the circulation liquid. Additionally, the flow rate of a liquid that circulates can be stably secured by preventing the circulation liquid itself from volatilizing to decrease the amount thereof, and this contributes to maintaining stable circulation efficiency.

The circulating pump 110 is equipped with a laminated piezoelectric element 114, a piezoelectric element case 112 that houses the piezoelectric element 114 therein, and a channel case 140 that has a channel formed therein. The piezoelectric element 114 has a bottom portion fixed to the piezoelectric element case 112. A circular reinforcing plate 116 is attached to an upper end of the piezoelectric element 114, and a circular diaphragm 118 formed from a metal sheet or the like is bonded to an upper face of the reinforcing plate 116. The reinforcing plate 116 reinforces the strength of the diaphragm 118. The thickness of the reinforcing plate 116 is set so that a lower face of the diaphragm 118 is in contact with an upper end face of the piezoelectric element case 112.

A recess 140C is formed on the lower face side (side that faces the piezoelectric element case 112) of the channel case 140, and an annular member 120 is fitted into the recess 140C. The internal diameter of the annular member 120 is smaller than the external diameter of the diaphragm 118. If the piezoelectric element case 112 and the channel case 140 are made to face each other and are fixed by screwing or the like, the diaphragm 118 is pinched between the annular member 120 and the piezoelectric element case 112, and the airtightness between the channel case 140 and the diaphragm 118 is brought into the state of being secured by the annular member 120. As a result, a pump chamber 130, which is the space surrounded by the recess 140C of the case 140, the inner peripheral surface of the annular member 120, and the diaphragm 118, is formed. The volume of the pump chamber 130 changes as the piezoelectric element 114 elongates or shrinks and the diaphragm 118 is deformed.

In the channel case 140, a liquid chamber 146 that guides a liquid to the pump chamber 130, a pump discharge channel 142 that is connected to one end of the liquid channel 190 and guides the liquid within the pump chamber 130 to the liquid channel 190, and a pump suction channel 144 that is connected to the other end of the liquid channel 190 and guides the liquid supplied from the liquid channel 190 to the liquid chamber 146 are further formed.

The liquid chamber 146 is formed so that one end opens to the upper face side (the side opposite to the side that faces the piezoelectric element case 112) of the channel case 140, the other end communicates with the pump chamber 130, and the diameter decreases toward the pump chamber 130 side (the cross-sectional area becomes smaller). The pump suction channel 144 is connected to a portion where the diameter of the liquid chamber 146 decreases. A check valve 148 is provided at the end portion of the liquid chamber 146 on the pump chamber 130 side. The check valve 148 permits the inflow of a liquid from the liquid chamber 146 to the pump chamber 130 and prevents the backflow of the liquid from the pump chamber 130 to the liquid chamber 146.

A film pack 160 is airtightly connected to an opening portion of the liquid chamber 146 formed on the upper face side of the channel case 140 via a connecting member 162. The film pack 160 is formed from a flexible film having gas barrier properties and heat resistance in order to prevent mixing of bubbles in the circulation liquid. In addition, in the present example, the film pack 160 is attachable to and detachable from the channel case 140, and replacement of the film pack, exclusion of bubbles within the film pack, and replenishment of the liquid becomes easy. In addition, depending on the circulation liquid, the film does not need to have gas barrier properties or heat resistance, and the material of a film is appropriately selected. Additionally, in the present example, the film pack 160 is made attachable to and detachable from the channel case 140. However, the film pack 160 may be formed integrally with the channel case 140.

The liquid circulating device 100 configured as described above circulates the liquid within the liquid channel 190 by driving the piezoelectric element 114 of the circulating pump 110. Next, the operation of the circulating pump 110 will be described in detail.

A2. Operation of Circulating Pump 110:

FIGS. 3A to 3C are explanatory views showing the flow of a liquid inside the circulating pump 110. FIG. 3A is an explanatory view showing a state (state before a driving voltage is applied to the piezoelectric element 114) where the circulating pump 110 is not operating. Hereinafter, the state where the circulating pump 110 is operating is also referred to as an operating state, and a state where the circulating pump 110 is not operating is also referred to as a stopped state. In the stopped state, the pump chamber 130 is not filled with the liquid. Additionally, in the stopped state, a predetermined amount of liquid is contained in advance even in the film pack 160. In the stopped state, the pressure inside the pump chamber 130, the film pack 160, and the liquid channel 190 is almost equal to the atmospheric pressure. The liquid (hereinafter referred to as a pressure regulation liquid BF) contained within the film pack 160 in the stopped state is used in order to regulate the inside of the liquid channel 190 to an appropriate pressure in the operating state. The pressure regulation liquid BF will be described below in detail.

FIG. 3B is an explanatory view showing a state where a driving voltage is applied to the piezoelectric element 114. If a driving voltage is applied to the piezoelectric element 114 in a state where the pump chamber 130 is filled with the liquid, the piezoelectric element 114 elongates due to the applied driving voltage and pushes up the diaphragm 118 in the direction of the pump chamber 130 via the reinforcing plate 116. If the pump chamber 130 is pushed by the diaphragm 118, the volume of the pump chamber 130 decreases and the liquid within the pump chamber 130 is pressurized. At this time, since the check valve 148 is brought into a closed state and the backflow of the liquid from the pump chamber 130 to the liquid chamber 146 is prevented, an amount of liquid equivalent to the decreased volume of the pump chamber 130 is pumped toward the liquid channel 190 through the pump discharge channel 142.

If the liquid is sent into the liquid channel 190 in this way, the liquid within the liquid channel 190 is gradually washed away to the downstream side. Additionally, as described above, in the liquid circulating device 100 of the present example, a closed system is constituted by the liquid channel 190 and the circulating pump 110, and the liquid that has been pushed out from the liquid channel 190 and has returned to the circulating pump 110 flows into the film pack 160 through the pump suction channel 144. Here, the film pack 160 is formed from a flexible film, is not in the state of being filled with the liquid and being completely stretched, and is attached in a state where a margin to expand is still left behind. Accordingly, even if the liquid that has returned from the liquid channel 190 flows into the film pack 160, as the film pack 160 expands, the pressure within the film pack 160 or the liquid chamber 146 that communicates with the film pack 160 is kept from increasing.

FIG. 3C is an explanatory view showing a state where a driving voltage to be applied to the piezoelectric element 114 has decreased. If the driving voltage decreases, the piezoelectric element 114 shrinks and returns to its original length. Then, the volume of the pump chamber 130 increases (restores to its original volume). At this time, since the inside of the pump chamber 130 has a negative pressure, the check valve 148 is brought into an open state, and the liquid is suctioned into the pump chamber 130 from the liquid chamber 146. In addition, the negative pressure means a pressure equal to or lower than the atmospheric pressure.

The negative pressure in the pump chamber 130 also acts on the pump discharge channel 142. However, the channel resistance of the pump discharge channel 142 is defined as being greater than the channel resistance of the liquid chamber 146 or the check valve 148. Accordingly, compared to the pump discharge channel 142, the liquid easily flows into the pump chamber 130 from the liquid chamber 146. Additionally, since the liquid chamber 146 communicates with the film pack 160, and the liquid within the film pack 160 flows into the pump chamber 130 without stagnation, the inside of the liquid chamber 146 is unlikely to have a negative pressure.

If the piezoelectric element 114 elongates again due to an increase in the driving voltage after the pump chamber 130 whose volume is restored is filled with the liquid from the liquid chamber 146 in this way, as shown in FIG. 3B, the liquid pressurized within the pump chamber 130 is pumped toward the pump discharge channel 142 and the liquid channel 190. As the circulating pump 110 repeats the above operation, the liquid circulating device 100 circulates the liquid within the liquid channel 190.

A3. Configuration of Film Pack:

FIGS. 4A to 4D are explanatory views showing the configuration of the film pack 160. An exploded perspective view of the film pack 160 is shown in FIG. 4A. The film pack 160 is constituted by a pair of flexible films 164 having gas barrier properties and heat resistance, a connecting member 162 that has a communication hole 162 a and detachably connect the film pack 160 to the liquid chamber 146, and an open port member 166 that is provided with an open port that can be opened and closed. The pair of films 164 are formed in a substantially rectangular shape. The film pack 160 is formed by pinching the connecting member 162 on one end side of the pair of films 164 in the longitudinal direction, pinching the open port member 166 on the other end side, and airtightly sticking the peripheries of the films together by thermocompression bonding or the like.

The film pack 160 formed by sticking the pair of films 164 together is shown in FIG. 4B. In addition, in FIG. 4B, a sealed portion stuck by thermocompression bonding or the like is shown in a hatched fashion. As shown in FIG. 4B, the film pack 160 is brought into a state where the pair of films 164 are in contact with each other in a state where the liquid is not contained inside the film pack.

In contrast, if the liquid flows into the film pack 160 through the communication hole 162 a of the connecting member 162, as shown in FIG. 4C, the film pack 160 expands (volume increases) as the pair of films 164 are separated from each other. Thus, the liquid can be contained in the film pack. Additionally, if the liquid within the film pack 160 flows out through the communication hole 162 a of the connecting member 162, the pair of films 164 approach each other, and the film pack 160 contracts (volume decreases). In this way, since the film pack 160 is easily deformable according to the amount of the liquid to be contained therein, the pressure of the liquid inside the film pack can be maintained in a predetermined range.

The structure of the film 164 used for the film pack 160 is illustrated in FIG. 4D. The shown film 164 has a multilayer structure, and adopts a structure in which polypropylene (PP) layers having excellent water-proofing characteristics are stuck on both sides of aluminum foil (AL) and polyethylene terephthalate (PET) layers having excellent shock resistance are further stuck on both sides from on the polyprolylene layers. The respective layers are pasted together by an adhesive. By providing a middle layer of aluminum foil, the strength of the film can be enhanced and gas barrier properties can also be enhanced. The film pack 160 of such a configuration has excellent heat resistance, has handleability at a high temperature (for example, 150° C.), has flexibility, and is easily deformed. Since the deformation of the film pack 160 is easy, even if there is a case that covers the circulating pump 110, the film pack can be deformed within the case. As a result, since the shape of the case is not easily restricted, the case that covers the circulating pump 110 can be made small. Additionally, weight reduction can be realized, and the film pack 160 can be simply formed by thermocompression bonding, which is economical. Moreover, since the film pack 160 is attachable to and detachable from the liquid chamber 146, it is easy to replace the film pack 160, which is economical.

The structure of the film 164 used for the film pack 160 is not limited to the structure shown in FIG. 4D. For example, instead of the aluminum foil as the middle layer, ethylene-vinyl alcohol copolymer resin (EVOH), polyvinylidene chloride (PVDC), or the like may be used. Additionally, a transparent film, obtained by directly sticking the outer layer of polyamide (nylon) and the inner layer of polypropylene (PP) together with an adhesive, may be used. By making a part or the whole of the film pack 160 transparent, it is possible to visually recognize the inside of the film pack 160 (the amount of the liquid and flow of the liquid).

A4. Pressure Regulation liquid BF:

Next, the pressure regulation liquid BF will be described. The pressure regulation liquid BF is supplied from the film pack 160 to the liquid chamber 146 as a part of the liquid that circulates, in order to maintain the inside of the liquid channel 190 at an appropriate pressure, when the circulating pump 110 is brought into the operating state from the stopped state. In the present example, the phrase “maintaining the inside of the liquid channel 190 at an appropriate pressure” means maintaining the pressure inside the liquid channel 190 (hereinafter referred to as an internal pressure) at the atmospheric pressure or higher in the operating state of the circulating pump 110. As the internal pressure of the liquid channel 190 is maintained at the atmospheric pressure or higher by the pressure regulation liquid BF, a situation in which the liquid channel 190 is deformed inward due to the force of the atmospheric pressure and the channel becomes narrow is avoided. As a result, in the circulating pump 110, a decrease in the circulation efficiency of the liquid that circulates is avoided by the pressure regulation liquid BF.

The principle in which the internal pressure of the liquid channel 190 is appropriately maintained as the pressure regulation liquid BF is supplied to the liquid chamber 146 will be described. FIG. 5 is an explanatory view schematically illustrating the distribution of the internal pressure and a shape in the liquid channel 190 where the internal pressure is appropriately maintained.

A model (internal pressure investigation model) of the liquid circulating device 100 for investigating the internal pressure of the liquid channel 190 is shown in an upper portion of FIG. 5. As shown in this drawing, in the internal pressure investigation model, the liquid channel 190 is shown on a straight line in order to facilitate investigation. Additionally, an end point of the liquid channel 190 connected to the pump discharge channel 142 is defined as a channel start point S, and an endpoint that is used as the pump suction channel 144 is defined as a channel end point E. Moreover, the length of the liquid channel 190 from the channel start point S to the channel end point E is defined as L. In addition, although the channel end point E and the pump suction channel 144 are shown in FIG. 5 so as to be separated, the channel end point E and the pump suction channel 144 are connected in the actual liquid circulating device 100. The arrow of a broken line shown in the drawing indicates the direction in which the liquid flows. Additionally, the internal pressure of the channel start point S in the operating state of the circulating pump 110 is defined as pressure Pout, and the internal pressure of the channel end point E in the operating state of the circulating pump 110 is defined as Pin.

The circulating pump 110 pressurizes the liquid that has flowed into the pump chamber 130 from the pump suction channel 144, and pumps the liquid toward the liquid channel 190 from the pump discharge channel 142. Then, a pressure gradient is formed in the internal pressure of the liquid channel 190 by the pumping of the liquid using the circulating pump 110, and the liquid flows depending on the formed pressure gradient. In the internal pressure investigation model, the pump chamber 130 applies the pressure of ΔPs further by driving of the piezoelectric element 114 to the liquid that has flowed into the pump chamber 130 with the internal pressure Pin. Accordingly, the relationship of Pin+ΔPs=Pout is established in the internal pressure investigation model. In the present example, the internal pressure of the liquid channel 190 is investigated using such an internal pressure investigation model.

An internal pressure distribution model of the liquid channel 190 in a state where the internal pressure is appropriate is shown in a middle portion of FIG. 5. In the internal pressure distribution model, the horizontal axis is defined as the position x from the channel start point S in the liquid channel 190, and the vertical axis is defined as the internal pressure P(x) at the position x. As described above, in the present example, the state where the internal pressure is appropriate means that the internal pressure is equal to or higher than the atmospheric pressure. Accordingly in the internal pressure distribution model in the present example, the internal pressure Pin in the channel end point E (x=L) where the internal pressure becomes the lowest is defined as the atmospheric pressure. In FIG. 5, the pressure is expressed as the relative atmospheric pressure (on the basis of the atmospheric pressure). In this case, if the relationship of Pin+ΔPs=Pout described above is taken into consideration, the internal pressure in the channel start point S becomes Pout=Ps.

Additionally, in the present example, the pressure gradient in the liquid channel 190 adopts a linear model. Accordingly, the relationship between P(x) and the position x can be expressed by the following Formula (5). Such an internal pressure distribution model is adopted in the present example. Additionally, in the present example, although P(x) is linear, P(x) has a decay curve or a quadratic curve.

$\begin{matrix} {{P(x)} = {{{- \frac{Ps}{L}}x} + {Ps}}} & (5) \end{matrix}$

A shape schematic view of the liquid channel 190 in a state where the internal pressure is appropriate is shown in a lower portion of FIG. 5. That is, the shape of the liquid channel 190 in a case where the internal pressure is distributed like P(x) shown in the middle portion of FIG. 5 is schematically shown. As shown in the drawing, the shape of the liquid channel 190 before the internal pressure changes (stopped state) is shown by a broken line, and a portion where the shape of the liquid channel 190 has changed depending on a change in the internal pressure caused by the operation of the circulating pump 110 is shown by a slanting line. In addition, the internal pressure in the stopped state is almost uniformly the atmospheric pressure. As described above, the liquid channel 190 is a flexible tube. In this case, since the internal pressure is equal to or higher than the atmospheric pressure, the liquid channel 190 is distorted toward the outside due to an outward force caused by a pressure differential. That is, in a case where the internal pressure changes as shown in the middle portion of FIG. 5, the liquid channel 190 expands and the volume inside the liquid channel 190 becomes large. If Young's modulus of the tube that constitutes the liquid channel 190 is uniform without depending on the position x, the outward distortion amount of the liquid channel 190 at each position x of the liquid channel 190 becomes a value according to the magnitude of the internal pressure P(x) at each position x. Since the internal pressure is linear with respect to the position x of the liquid channel 190, the distortion amount of the liquid channel 190 also becomes linear with respect to the position x.

Here, the relationship of the following Formula (6) is established if the ratio of the internal pressure P(x) of the liquid channel 190 and the increased amount of the cross-sectional area of the channel is defined as Se, and the amount of volume change of the liquid channel 190 per minute length Δx is defined as ΔVe(x), when the internal pressure has changed from a state (stopped state of the circulating pump 110) where the internal pressure is uniformly the atmospheric pressure to a state (operating state of the circulating pump 110) of the internal pressure distribution shown in FIG. 5. In addition, Se is a constant that is determined depending on Young's modulus, Poisson's ratio, internal diameter, and external diameter of the tube that constitutes the liquid channel 190, and is constant irrespective of the position x of the channel.

ΔVe(x)=Se·P(x)·dx  (6)

Accordingly, if the amount of volume change in the total (length L) of the liquid channel 190 is defined as ΔVs, ΔVs is expressed as the following Formula (7).

ΔVs=∫ ₀ ^(L) ΔVe(x)=∫₀ ^(L) Se·P(x)dx  (7)

Moreover, if the compliance of the liquid channel 190 is defined as Cs, since the compliance Cs is the ratio of the internal pressure and the increased amount of the internal volume when the internal pressure is uniformly applied to the liquid channel 190, the compliance is expressed by multiplying Se by the tube length L. Accordingly, since the relationship of the following Formula (8) is established, Formula (7) can be expressed as the following Formula (9).

$\begin{matrix} {{Cs} = {L \cdot {Se}}} & (8) \\ {{\Delta \; {Vs}} = {\frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot {P(x)}}\ {x}}}}} & (9) \end{matrix}$

Additionally, if Formula (5) is applied as the internal pressure P(x), Formula (9) is expressed as the following Formula (10).

$\begin{matrix} {{\Delta \; {Vs}} = {{\frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot \left( {{{- \frac{Ps}{L}}x} + {Ps}} \right)}{x}}}} = {\frac{1}{2}{{Cs} \cdot {Ps}}}}} & (10) \end{matrix}$

That is, by further supplying the liquid of ΔVs (=½·Cs·Ps) to the liquid channel 190 compared to the stopped state, the inside of the liquid channel can be maintained at an appropriate pressure and the circulating pump 110 can be operated. In the present example, the pressure regulation liquid BF that is contained in advance in the film pack 160 is used as a liquid corresponding to the amount of volume change ΔVs of the liquid channel 190. Specifically, the pressure regulation liquid BF is contained in the film pack 160 in the stopped state of the circulating pump 110, and the pressure regulation liquid BF is supplied to the liquid chamber 146 in the operating state of the circulating pump 110.

A value that satisfies the following Formula (11) is applied as the volume Vb of the pressure regulation liquid BF to be contained in the film pack 160 in the stopped state of the circulating pump 110. In addition, in Formula (11), γ is a coefficient. The coefficient γ is set to 0.8 or less in consideration of the fact that the circulating pump 110 operates even in a case where the volume Vb of the pressure regulation liquid BF to be contained in the film pack 160 is slightly smaller than the amount of volume change ΔVs of the liquid channel 190.

Vb=γ·ΔVs

(γ≧0.8)  (11)

The pressure regulation liquid BF with the volume Vb contained in the film pack 160 is automatically supplied into the pump chamber 130 by the atmospheric pressure applied to the film pack 160, if the circulating pump 110 starts to operate. Specifically, this is based on the following principle.

If the operation of the circulating pump 110 is started, a pressure gradient is formed in the internal pressure of the liquid channel 190. The pressure gradient of the internal pressure deforms the liquid channel 190. In that case, the internal pressure (Pout) of the channel start point S in the liquid channel 190 increases due to the pressurization of ΔPs by the circulating pump 110. As a result, the liquid channel 190 in the vicinity of the channel start point S expands. If the channel start point S of the liquid channel 190 expands, since the liquid moves in a direction in which the volume of the liquid that has expanded is compensated for, the volume of the liquid in the vicinity of the channel end point E becomes less, and the internal pressure in the vicinity of the channel end point E decreases. In that case, the pressure regulation liquid BF is supplied to the liquid chamber 146 from the film pack 160 due to the pressure differential between the vicinity of the channel endpoint E and the inside of the film pack 160. Then, the amount of volume change ΔVs of the liquid channel 190 is compensated for by the pressure regulation liquid BF of the volume Vb supplied, and the internal pressure of the liquid channel 190 is maintained in an appropriate state. Additionally, if the volume Vb of the pressure regulation liquid BF to be contained in the film pack 160 is insufficient, channel deformation in the direction of the inside of the liquid channel 190 is caused by the atmospheric pressure. However, in a range (0.8≦γ<1) slightly smaller than the amount of volume change ΔVs of the liquid channel 190, the channel deformation to the direction of inside of the liquid channel 190 by the atmospheric pressure does not become a large resistance element even if the deformation is caused more or less. Therefore, the circulation efficiency of the liquid by the circulating pump 110 does not decrease significantly.

As described above, the liquid circulating device 100 contains the pressure regulation liquid BF in the film pack 160 in advance in the stopped state of the circulating pump 110. Then, when the circulating pump 110 operates, the pressure regulation liquid BF is supplied to the liquid chamber 146 from the film pack 160, and the pressure regulation liquid BF compensates for the amount of volume change ΔVs of the liquid channel 190. Accordingly, during the operation of the circulating pump 110, the pressure regulation liquid BF keeps the internal pressure of the liquid channel 190 from becoming significantly lower than the atmospheric pressure, and the channel deformation in the direction of the inside of the liquid channel 190 by the atmospheric pressure is avoided. As a result, in the liquid circulating device 100, the channel cross-sectional area of the liquid in the liquid channel 190 can be sufficiently secured, and a decrease in the circulation efficiency can be prevented. Additionally, since the pressure regulation liquid BF contained in the film pack 160 is automatically supplied to the liquid chamber 146 by the pressure differential between the internal pressure in the vicinity of the channel endpoint E and the atmospheric pressure applied to the film pack 160, it is not necessary to control the supply of the pressure regulation liquid BF separately using a pressure sensor or the like.

Additionally, if the liquid circulating device 100 is not equipped with the film pack 160, it is better to replenish the liquid channel 190 with the liquid of the volume Vb in the stopped state of the circulating pump 110 and keep the internal pressure from becoming equal to or higher than the atmospheric pressure in the stopped state, in order to maintain the internal pressure in an appropriate state in the operating state. In this case, since the liquid channel 190 has a state where the liquid channel has expanded from a normal shape as a steady state in the stopped state, and consequently, load is added to the liquid channel 190, the durability of the whole liquid channel 190 (particularly, in the vicinity of the channel end point E) decreases. In the liquid circulating device 100 in the present example, the pressure regulation liquid BF is contained in the film pack 160 in the stopped state of the circulating pump 110. Thus, the internal pressure can be maintained at the atmospheric pressure in the liquid channel 190 in the stopped state of the circulating pump 110, and application of unnecessary load to the liquid channel 190 due to the internal pressure can be avoided. Thus, the durability particularly in the vicinity of the channel end point E improves.

B. Second Example

Next, a second example of the invention will be described. In a second example, as the liquid circulating device, a liquid circulating device 200 is used instead of the liquid circulating device 100. In the liquid circulating device 100 in the first example, the pressure regulation liquid BF is contained in the film pack 160. However, in the liquid circulating device 200 in the second example, instead of the film pack 160, the pressure regulation liquid BF is contained in a branch channel 210 provided in the liquid channel 190. Since components other than the branch channel 210 are the same as those of the first example, description of the components other than the branch channel 210 is omitted. In addition, the same reference numerals are given to the same components in the first example and the second example.

FIG. 6 is an explanatory view illustrating the configuration of the branch channel 210 in the present example. The branch channel 210 is provided at the position of the liquid channel 190 near the pump suction channel 144. The branch channel 210 has high gas barrier properties, and is made of such materials that the liquid therein does not volatilize easily. The liquid that circulate through the liquid channel 190 by the operation of the circulating pump 110, including the pressure regulation liquid BF, is contained within the branch channel 210. Hereinafter, the liquid that circulates through the circulating pump 110 and the liquid channel 190 is also referred to as a first liquid Lq1.

The branch channel 210 is installed so that the position of the liquid head of the first liquid Lq1 becomes a position higher than the circulating pump 110. The first liquid Lq1 of the volume Vb is contained within the branch channel 210, and functions as the pressure regulation liquid BF in the operating state of the circulating pump 110.

As shown in the drawing, the branch channel 210 has therein a movable portion 216. The branch channel 210 has a vent hole 218 as an air flow passage, and is configured so that the movable portion 216 is in contact with the open air. The movable portion 216 is constituted by a second liquid Lq2 and a high-viscosity gel liquid 214. The second liquid Lq2 is located in contact with the liquid head of the first liquid Lq1. If the position of the liquid head of the first liquid Lq1 moves, the movable portion 216 moves in a height direction of the branch channel 210 where the movable portion is in contact with the first liquid Lq1. The inner wall surface of the branch channel 210 has a smooth surface so that the movement of the movable portion 216 is smooth. Additionally, the liquid circulating device 200 is equipped with a sensor 230 that can measure the travel distance of the movable portion 216, in the vicinity of the branch channel 210, and can measure the travel distance of the movable portion 216.

The high-viscosity gel liquid 214 that is a constituent element of the movable portion 216 is enclosed as a sealing material for preventing leakage of the first liquid Lq1 from the branch channel 210, and preventing evaporation. The high-viscosity gel liquid 214 has polybutene of an average molecular weight of 630 as a base material, and has visco-elasticity and transparency. As for the type of high-viscosity gel liquid 214, polybutene, α-olefin, or the like of an average molecular weight of 300 to 3700 can be used.

Additionally, it is desirable that the high-viscosity gel liquid 214 not be substantially compatible with the first liquid Lq1. In a case where an oily medium is used as the first liquid Lq1, an aqueous high-viscosity gel that contains water as a medium can be used. In a case where the aqueous high-viscosity gel liquid 214 is used, an oily layer that contains an organic solvent as a solvent may be further formed on the high-viscosity gel liquid 214 to prevent permeation and drying in a case where the gas permeability of the high-viscosity gel liquid 214 is high or in a case where the gel liquid is apt to be dried.

The second liquid Lq2 is contained in the branch channel 210 in order to prevent the high-viscosity gel liquid 214 from dissolving in the first liquid Lq1. The second liquid Lq2 is a liquid with a greater vaporization heat than the first liquid Lq1, and is a liquid that is phase-separable from the first liquid Lq1. Additionally, the second liquid Lq2 has a density smaller than the first liquid Lq1. In the present example, fluidized paraffin is used as the second liquid Lq2. In addition, calcium alginate can also be used as the second liquid Lq2. As the movable portion 216 has the above configuration, the first liquid Lq1 does not come into direct contact with the atmospheric air.

In the liquid circulating device 200 of the configuration described above, if the circulating pump 110 operates, a pressure gradient is formed in the internal pressure of the liquid channel 190 as described in the first example. Then, the pressure in the vicinity of the channel endpoint E of the liquid channel 190 decreases due to a change in the volume of the liquid channel 190. The first liquid Lq1 (equivalent to the pressure regulation liquid BF) within the branch channel 210 is supplied to the liquid channel 190 by the pressure differential between the internal pressure in the vicinity of the channel end point E and the atmospheric pressure applied to the branch channel 210. As a result, the internal pressure of the liquid channel 190 can be kept equal to or higher than the atmospheric pressure, and the circulating pump 110 can operate with the internal pressure in an appropriate state.

As described above, the liquid circulating device 200 includes the branch channel 210 that stores the first liquid Lq1 as the pressure regulation liquid BF. Thus, similarly to the first example, in the operating state of the circulating pump 110, the internal pressure of the liquid channel 190 can be kept from becoming significantly lower than the atmospheric pressure, and the liquid circulating device can operate in an appropriate state. Additionally, since the branch channel 210 is equipped with the movable portion 216, the first liquid Lq1 can be prevented from leaking to the outside from the branch channel, and the first liquid Lq1 can be prevented from evaporating.

Additionally, since the liquid circulating device 200 is equipped with the sensor 230, the liquid circulating device can measure the travel distance of the movable portion 216 when the circulating pump 110 changes from the stopped state to the operating state. Also, it is possible to acquire the amount of the first liquid Lq1 supplied to the liquid channel 190 as the pressure regulation liquid BF on the basis of the measured travel distance of the movable portion 216. Since the supply amount of the pressure regulation liquid BF is equal to the amount of volume change of the liquid channel 190, it is consequently possible to acquire the state of the internal pressure of the liquid channel 190 in the operating state in real time.

C. Modification Examples

The invention is not limited to the above examples or embodiments, and can be carried out in various aspects without departing from the scope of the invention. For example, the following modifications can also be made.

C1. Modification Example 1

In the above examples, the liquid circulating device 100 is utilized for cooling the piezoelectric actuator 34 of the liquid ejecting apparatus 20 (water jet knife). However, the liquid circulating device 100 may be utilized for adjusting the temperature of other medical apparatuses other than the water jet knife. For example, the liquid circulating device 100 may be utilized for adjusting the temperature of a motor section of a medical drill, an ultrasonic wave generating section of an ultrasonic scaler that removes plaque with an ultrasonic wave, or the like, or may be an ejecting apparatus that ejects a medical fluid to a living body. Additionally, the liquid circulating device 100 may be used not only when cooling a heat generator but when heating an object. For example, the liquid circulating device may be used when heating or keeping warm a part of a human body. This can be realized by separately equipping the above liquid circulating device 100 with a heating section that heats a circulation liquid. Particularly, since the liquid circulating device 100 ensures the stable circulation efficiency in medical apparatuses in which safety is regarded as important, the liquid circulating device can be applied to the medical apparatuses.

C2. Modification Example 2

In the above examples, a liquid, particularly water, is adopted as the liquid that circulates through the liquid circulating device 100. However, the liquid is not limited to this, and various liquids can be adopted. For example, nitrogen or carbon dioxide may be adopted as gas. Additionally, oil, other than water may be used as the liquid, and the liquid is not limited to water or oil as long as heat exchange is possible.

C3. Modification Example 3

In the above examples, the film pack is adopted as the liquid containing chamber. However, the liquid containing chamber is not limited to this. For example, a liquid containing chamber including a housing that has a diaphragm may be adopted. In addition, a liquid containing chamber, which is deformable according to the amount of a liquid to be contained, such as an elastic bag-shaped rubber pack or bellows, may be adopted. Even if such a liquid containing chamber is adopted, the same effects as the above examples can be obtained.

C4. Modification Example 4

In the second example, the branch channel 210 is equipped with the movable portion 216. However, a branch channel that is not equipped with the movable portion may be adopted. This can simplify the configuration of the branch channel.

C5. Modification Example 5

In the above examples, the piezoelectric element is adopted as an operating element. However, the operating element is not limited to this, and various elements may be adopted. For example, drive elements, such as an electrostrictive element, an electromagnetic actuator, an electrostatic actuator, and a dielectric poly-actuator, can be used. Even if these drive elements are adopted, the same effects as the above examples can be obtained. Additionally, in the above examples, a laminated piezoelectric element is adopted as the piezoelectric element. In addition, however, a piezoelectric element that is a crystal single body, a mono-morph piezoelectric element, or a bimorph piezoelectric element may be adopted.

C6. Modification Example 6

In the above examples, the check valve 148 is adopted as a liquid resistance element. However, the liquid resistance element is not limited to this, and various liquid resistance elements may be adopted. FIGS. 7A to 7C are explanatory views showing liquid resistance elements that can be adopted. The shown liquid resistance element (A) is a check valve installed at a position different from the first example. A liquid resistance element (B) suppresses the flow of the liquid from the pump chamber 130 to the liquid chamber 146, without using the check valve. A liquid resistance element (C) has a configuration in which the check valve 148 is not installed in the above examples. Even in the liquid resistance element (C), the flow of the liquid from the pump chamber 130 to the liquid chamber 146 can be suppressed depending on the shape of the liquid resistance element. Additionally, since the liquid resistance element (B) and the liquid resistance element (C) do not have the movable portion such as the check valve 148, durability can be improved.

This application claims priority to Japanese Patent Application No. 2012-059234 filed on Mar. 15, 2012, and Application No. 2012-249060 filed on Nov. 13, 2012, the entirety of which is hereby incorporated by reference. 

What is claimed is:
 1. A medical apparatus that circulates a liquid in non-contact with the atmospheric air, comprising: a pump chamber whose volume is changed by a volume changing unit; an inlet channel that is an inflow passage of the liquid to the pump chamber; a liquid resistance element that controls or stops the flow of the liquid that flows from the pump chamber to the inlet channel; an outlet channel that is an outflow port of the liquid from the pump chamber; a circulation channel of a length L through which the liquid circulates from the outlet channel to the inlet channel; and a pressure regulating mechanism that contains the liquid of a volume Vb during the non-operation of the volume changing unit and supplies the contained liquid as part of the circulating liquid during the operation of the volume changing unit, wherein when the compliance of the circulation channel is defined as Cs, and the pressure of the liquid in the circulation channel at the position of a length x from the outlet channel during the operation of the volume changing unit is defined as P(x), the volume Vb satisfies the relationship of Formula (1): $\begin{matrix} {{Vb} \geq {\gamma \frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot {P(x)}}\ {{{x\left( {\gamma \geqq 0.8} \right)}}.}}}}} & (1) \end{matrix}$
 2. The medical apparatus according to claim 1, wherein the volume Vb satisfies the relationship of Formula (2) when the pressure of the liquid that flows into the circulation channel from the outlet channel is defined as Ps: Vb≧γ½Cs·Ps (γ≧0.8)  (2)
 3. The medical apparatus according to claim 1, wherein the pressure regulating mechanism includes a liquid containing chamber that contains the liquid to be used for the supply, and is deformable according to the amount of the liquid contained inside the liquid containing chamber.
 4. The medical apparatus according to claim 3, wherein the liquid containing chamber is a pack formed by sealing films in the shape of a bag.
 5. The medical apparatus according to claim 4, wherein the liquid containing chamber is attachable to and detachable from the liquid circulating device.
 6. The medical apparatus according to claim 1, wherein the pressure regulating mechanism includes a branch channel that branches from the circulation channel.
 7. The medical apparatus according to claim 6, wherein a sealing material that seals the contained liquid moves according to the pressure differential between the pressure of the liquid within the branch channel and the atmospheric pressure is arranged inside the branch channel.
 8. The medical apparatus according to claim 7, wherein the liquid is a first liquid, a second liquid that is phase-separable from the first liquid is sealed between the first liquid and the sealing material inside the branch channel, and the vaporization heat of the second liquid is greater than the vaporization heat of the first liquid.
 9. The medical apparatus according to claim 1, wherein the volume changing unit uses an operating element that operates depending on a change in voltage.
 10. A medical apparatus circulates a liquid in non-contact with the atmospheric air according to claim
 1. 11. A liquid circulating device comprising: a pump chamber whose volume is changed by a volume changing unit; an inlet channel that is an inflow passage of the liquid to the pump chamber; a liquid resistance element that controls or stops the flow of the liquid that flows from the pump chamber to the inlet channel; an outlet channel that is an outflow port of the liquid from the pump chamber; a circulation channel of a length L through which the liquid circulates from the outlet channel to the inlet channel; and a pressure regulating mechanism that contains the liquid of a volume Vb during the non-operation of the volume changing unit and supplies the contained liquid as part of the circulating liquid during the operation of the volume changing unit, wherein when the compliance of the circulation channel is defined as Cs, and the pressure of the liquid in the circulation channel at the position of a length x from the outlet channel during the operation of the volume changing unit is defined as P(x), the volume Vb satisfies the relationship of Formula (1): $\begin{matrix} {{Vb} \geq {\gamma \frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot {P(x)}}\ {{{x\left( {\gamma \geqq 0.8} \right)}}.}}}}} & (1) \end{matrix}$
 12. The medical apparatus according to claim 11, wherein the volume Vb satisfies the relationship of Formula (2) when the pressure of the liquid that flows into the circulation channel from the outlet channel is defined as Ps: Vb≧γ½Cs·Ps (γ≧0.8)  (2)
 13. The medical apparatus according to claim 11, wherein the pressure regulating mechanism includes a liquid containing chamber that contains the liquid to be used for the supply, and is deformable according to the amount of the liquid contained inside the liquid containing chamber.
 14. The medical apparatus according to claim 13, wherein the liquid containing chamber is a pack formed by sealing films in the shape of a bag.
 15. The medical apparatus according to claim 14, wherein the liquid containing chamber is attachable to and detachable from the liquid circulating device.
 16. The medical apparatus according to claim 11, wherein the pressure regulating mechanism includes a branch channel that branches from the circulation channel.
 17. The medical apparatus according to claim 16, wherein a sealing material that seals the contained liquid moves according to the pressure differential between the pressure of the liquid within the branch channel and the atmospheric pressure is arranged inside the branch channel.
 18. The medical apparatus according to claim 17, wherein the liquid is a first liquid, a second liquid that is phase-separable from the first liquid is sealed between the first liquid and the sealing material inside the branch channel, and the vaporization heat of the second liquid is greater than the vaporization heat of the first liquid.
 19. The medical apparatus according to claim 11, wherein the volume changing unit uses an operating element that operates depending on a change in voltage.
 20. A medical apparatus that circulates a liquid in non-contact with the atmospheric air, comprising: a pump chamber whose volume is changed by a volume changing unit; an inlet channel that is an inflow passage of the liquid to the pump chamber; an outlet channel that is an outflow port of the liquid from the pump chamber; a circulation channel of a length L through which the liquid circulates from the outlet channel to the inlet channel; and a pressure regulating mechanism that contains the liquid of a volume Vb during the non-operation of the volume changing unit and supplies the contained liquid as part of the circulating liquid during the operation of the volume changing unit, wherein when the compliance of the circulation channel is defined as Cs, and the pressure of the liquid in the circulation channel at the position of a length x from the outlet channel during the operation of the volume changing unit is defined as P(x), the volume Vb satisfies the relationship of Formula (1): $\begin{matrix} {{Vb} \geq {\gamma \frac{1}{L}{\int_{0}^{L}{{{Cs} \cdot {P(x)}}\ {{{x\left( {\gamma \geqq 0.8} \right)}}.}}}}} & (1) \end{matrix}$ 